Gas turbine

ABSTRACT

Gas turbine blade ring is cooled by steam of which temperature, pressure and flow rate are controlled so that clearance between moving blade tip and blade ring is maintained appropriately. Steam from steam turbine bottoming cycle ( 10 ) flows into blade ring cooling passage ( 8 ) of gas turbine ( 1 ) via piping ( 12 ) for cooling blade ring. The steam having cooled the blade ring is supplied into transition piece cooling passage ( 9 ) of combustor ( 3 ) for cooling transition piece and is then recovered into the steam turbine bottoming cycle ( 10 ) via piping ( 14 ). While the steam cools the blade ring, temperature, pressure and flow rate of the steam are controlled so that thermal elongation of the blade ring is adjusted and the clearance at the moving blade tip is controlled so as to approach target value. Thus, the clearance is maintained as small as possible in operation and gas turbine performance is enhanced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a gas turbine and moreparticularly to a gas turbine in which a blade ring, especially of firstand second stages, is improved in the shape so as to have less thermalinfluences as well as the blade ring is cooled with less thermalexpansion and uniform deformation by steam, of which temperature,pressure and flow rate are controlled, so that a clearance at a movingblade tip is reduced in operation, thereby enhancing a gas turbineperformance.

[0003] 2. Description of the Prior Art

[0004]FIG. 20 is a cross sectional view showing an interior of arepresentative gas turbine in the prior art. In FIG. 20, numeral 100designates an outlet of a combustor transition piece, from which a hightemperature combustion gas flows out. Numeral 101 designates a gas path,in which four stages of stationary blades 1C, 2C, 3C, 4C are arranged inan axial direction of the turbine. The stationary blades 1C, 2C, 3C, 4Care connected fixedly to blade rings 102, 103, 104, 105, respectively,via respective outer shrouds and each of the stationary blades 1C, 2C,3C, 4C includes a plurality of blades arranged in a circumferentialdirection of the turbine along respective inner walls of the blade rings102, 103, 104, 105. Also, moving blades 1S, 2S, 3S, 4S are arranged inthe axial direction alternately with the stationary blades 1C, 2C, 3C,4C and each of the moving blades 1S, 2S, 3S, 4S is connected fixedly toa rotor 200 and includes a plurality of blades arranged in thecircumferential direction around the rotor 200.

[0005] In the gas turbine of the above-mentioned construction, coolingof the blade is usually done by air such that the stationary blade isfed with cooling air from the blade ring side and the moving blade isfed with cooling air from the rotor side. Accompanying with a recenthigher temperature gas turbine, however, it is a tendency to employ acooling system using steam. Also, at the time of start-up of the gasturbine, while there is maintained a predetermined clearance between amoving blade tip and a blade ring, the blade ring is still cold toshrink in the rise time and, on the other hand, the rotor and the movingblade are heated earlier. Hence, the clearance at the moving blade tipbecomes smaller and a risk of contact in operation becomes higher.Accordingly, the clearance must be set appropriately taking this riskinto consideration. If this clearance is too broad, it will reduce thegas turbine performance and thus to make the clearance between themoving blade tip and the blade ring as small as possible is an effectivemeans to enhance the gas turbine performance. But it is still a presentstatus that such countermeasure is not sufficiently established yet inthe field of the industrial gas turbine.

[0006] As mentioned above, in the conventional industrial gas turbine,it is usual that cooling air is led into the gas turbine stationaryblade, moving blade, rotor, etc. for cooling thereof. But, in the recenttendency to employ a higher temperature gas turbine, a steam coolingsystem is being used in place of the air cooling system. In such a gasturbine, the clearance between the moving blade tip and the blade ringchanges due to thermal influences in the operation beginning from thestart-up time and the predetermined clearance at the start-up timebecomes the minimum clearance state caused by a thermal elongationdifference between the blade ring and the moving blade in the rise time,so that a contact may arise to invite a dangerous state unless anappropriate setting of the clearance is ensured. Also, if the clearanceis too large in operation, it will invite a reduction in the gas turbineperformance and so the appropriate setting of the tip clearance of themoving blade becomes necessary. For this purpose, it is preferable tomake the tip clearance not much changeable by heat as well as to makethe tip clearance optimally controlled so as not to cause a contact but,while such control is being variously studied, it is a present statusthat a sufficient art therefor is not established yet in the field ofthe industrial gas turbine.

SUMMARY OF THE INVENTION

[0007] In view of the mentioned problem in the prior art, it is anobject of the present invention to provide a gas turbine in which a gasturbine blade ring is improved in the structural shape so as to haveless thermal influences as well as the blade ring is made with a coolingsystem using steam of which temperature, pressure and flow rate arecontrolled so that a clearance between a moving blade tip and the bladering may be set optimally.

[0008] In order to achieve the mentioned object, the present inventionprovides means of the following (1) to (15):

[0009] (1) A gas turbine comprising a moving blade and a blade ringconfronting a tip of the moving blade, characterized in that a coolingpassage is provided in the blade ring and an auxiliary boiler and asteam supply source connecting to a steam turbine bottoming cycle areconnected to the cooling passage, so that steam of the auxiliary boileror the steam supply source is flown into the cooling passage for coolingthe blade ring and the steam having cooled the blade ring is recovered,and thereby a clearance between the tip of the moving blade and theblade ring is reduced.

[0010] (2) A gas turbine comprising a moving blade and a blade ringconfronting a tip of the moving blade as well as comprising a combustorand a transition piece contained in the combustor, characterized in thata cooling passage is provided in the blade ring, so that steam of asteam supply source is flown into the cooling passage for cooling theblade ring and the steam having cooled the blade ring is flown into thetransition piece via a combustor transition piece connection portion forcooling a wall interior of the transition piece and the steam havingcooled the wall interior of the transition piece is recovered into thesteam supply source, and thereby a clearance between the tip of themoving blade and the blade ring is reduced.

[0011] (3) A gas turbine comprising a moving blade and a blade ringconfronting a tip of the moving blade as well as comprising a combustorand a transition piece contained in the combustor, characterized in thata cooling passage is provided in the blade ring, so that steam of asteam supply source is flown in parallel into the cooling passage forcooling the blade ring and into the transition piece via a combustortransition piece connection portion for cooling a wall interior of thetransition piece and the steam having cooled the blade ring and the wallinterior of the transition piece is recovered into the steam supplysource, and thereby a clearance between the tip of the moving blade andthe blade ring is reduced.

[0012] (4) A gas turbine comprising a first stage stationary blade and afirst stage moving blade and a blade ring confronting a tip of the firststage moving blade as well as comprising a combustor and a transitionpiece contained in the combustor, characterized in that a blade ringcooling passage is provided in the blade ring and a stationary bladecooling passage is provided in the first stage stationary blade so as toconnect to the blade ring cooling passage, so that steam of a steamsupply source is flown into the blade ring cooling passage for coolingthe blade ring and the steam having cooled the blade ring is flown intothe stationary blade cooling passage for cooling the first stagestationary blade and the steam having cooled the first stage stationaryblade is flown into the transition piece via a combustor transitionpiece connection portion for cooling a wall interior of the transitionpiece and the steam having cooled the wall interior of the transitionpiece is recovered into the steam supply source, and thereby a clearancebetween the tip of the first stage moving blade and the blade ring isreduced.

[0013] (5) A gas turbine comprising a first stage stationary blade and afirst stage moving blade and a blade ring confronting a tip of the firststage moving blade as well as comprising a combustor and a transitionpiece contained in the combustor, characterized in that a blade ringcooling passage is provided in the blade ring and a stationary bladecooling passage is provided in the first stage stationary blade so as toconnect to the blade ring cooling passage, so that steam of a steamsupply source is flown in parallel into the blade ring cooling passagefor cooling the blade ring and into the stationary blade cooling passagefor cooling the first stage stationary blade and the steam having cooledthe first stage stationary blade is flown into the transition piece viaa combustor transition piece connection portion for cooling a wallinterior of the transition piece and the steam having cooled the bladering and the wall interior of the transition piece is recovered into thesteam supply source, and thereby a clearance between the tip of thefirst stage moving blade and the blade ring is reduced.

[0014] (6) A gas turbine as mentioned in (2) above, characterized inthat the blade ring is a blade ring confronting a tip of a first stagemoving blade, the combustor is a plurality of combustors arranged in aturbine circumferential direction, there are provided in the blade ringa plurality of blocks protruding in a turbine axial direction frompositions of the blade ring corresponding to positions of the pluralityof combustors and, in each of the plurality of blocks, there is provideda U-shape passage formed by turbine axial directional andcircumferential directional passages, so that steam is flown into theU-shape passage from one end of the U-shape passage for cooling theblade ring and is flown out of the other end of the U-shape passage, andthe steam having cooled the blade ring is supplied into the transitionpiece via the combustor transition piece connection portion.

[0015] (7) A gas turbine as mentioned in (2) above, characterized inthat the blade ring comprises a first blade ring confronting a firststage moving blade and a second blade ring confronting a second stagemoving blade, the cooling passage comprises a first cooling passageformed in the first blade ring and a second cooling passage formed inthe second blade ring and there are provided a turbine axial directionalpassage for connecting the first and second cooling passages to eachother and a transition piece side passage for connecting the firstcooling passage and the combustor transition piece connection portion toeach other, so that the steam of the steam supply source is flownsequentially in the second cooling passage, turbine axial directionalpassage, first cooling passage and transition piece side passage and isthen supplied to the combustor transition piece connection portion.

[0016] (8) A gas turbine as mentioned in (7) above, characterized inthat the combustor transition piece connection portion comprises atransition piece cooling inlet connecting to the first cooling passage,a transition piece cooling outlet through which the steam having cooledthe transition piece flows out and an outlet pipe manifold connecting tothe transition piece cooling outlet.

[0017] (9) A gas turbine as mentioned in (7) above, characterized inthat each of the first and second blade rings is formed such that upperand lower two separated semicircular portions of the blade ring arejoined together at flanges provided on both side surface portions of theblade ring, there are provided a recessed portion or a protruded portionon an outer circumferential surface portion of the blade ring so as tofit to or fit in a portion of a turbine casing inner wall and anotherprotruded portion on an inner circumferential surface portion of theblade ring so as to support a wall surface confronting the tip of themoving blade and a turbine axial directional cross sectional shape ofthe blade ring is approximately symmetrical relative to a turbine radialdirectional central axis in the turbine axial directional crosssectional shape of the blade ring.

[0018] (10) A gas turbine as mentioned in (7) above, characterized inthat each of the first and second blade rings is formed such that upperand lower two separated semicircular portions of the blade ring arejoined together at flanges provided on both side surface portions of theblade ring and, in horizontal surface portions of the upper and lowersemicircular portions of the blade ring so joined at the flanges, thecooling passage provided in the upper semicircular portion of the bladering is extended so as to be inserted with a predetermined length intothe cooling passage provided in the lower semicircular portion of theblade ring and a sealing material is interposed around the coolingpassage so extended of the upper semicircular portion of the blade ring.

[0019] (11) A gas turbine as mentioned in any one of (1) to (5) above,characterized in that the blade ring is formed such that upper and lowertwo separated semicircular portions of the blade ring are joinedtogether at flanges provided on both side surface portions of the bladering and there are provided members, having masses substantiallyequivalent to the flanges thermally, on upper and lower portions of anouter circumferential surface portion of the blade ring.

[0020] (12) A gas turbine as mentioned in any one of (1) to (5) above,characterized in that the blade ring is provided with a plurality ofsteam inlets and steam outlets, respectively, arranged substantiallyevenly in vertical and horizontal directions on an outer circumferentialsurface portion of the blade ring.

[0021] (13) A gas turbine as mentioned in (7) above, characterized inthat the blade ring is applied to on its surface exposed to a hightemperature space with a thermal shield made of a heat insulationmaterial.

[0022] (14) A gas turbine as mentioned in any one of (1) to (5) above,characterized in that the blade ring is provided therein with aplurality of sensors for sensing the clearance at the tip of the movingblade, the sensors being inserted from outside of a turbine casing topass through the turbine casing and the blade ring so that sensingportions of the sensors may be exposed on an inner circumferential wallsurface confronting the tip of the moving blade, and there are provideda steam temperature controller arranged in a route for supplying theblade ring with steam from the steam supply source, a steam flow controlvalve arranged between the steam temperature controller and a steaminlet of the blade ring and a control unit taking signals from thesensors for comparison with a predetermined target value and controllingthe steam temperature controller and an opening of the steam flowcontrol valve so that the clearance may be approached to the targetvalue.

[0023] (15) A gas turbine as mentioned in (14) above, characterized inthat the sensors are FM electrostatic capacity type sensors.

[0024] The present invention is based on the inventions mentioned in (1)to (5) above. In the invention (1), firstly at the start-up time, steamfrom the auxiliary boiler is supplied into the cooling passage of theblade ring so that the blade ring which is cold during the rise time isheated and the clearance at the moving blade tip is enlarged and therebya contact in the minimum clearance during the rise time can be avoided.In the ordinary operation time, steam from the steam turbine bottomingcycle is supplied into the blade ring to cool the portion of the bladering confronting the moving blade tip and, by setting the temperature,pressure and flow rate of the steam appropriately, thermal elongation ofthe blade ring is controlled so that the clearance at the moving bladetip may be set correctly and thereby the gas turbine performance isprevented from being reduced by enlargement of the clearance.

[0025] In the invention (2), the blade ring is first cooled and theclearance at the moving blade tip can be controlled appropriately. Andthen the steam which has cooled the blade ring is flown into thecombustor transition piece to flow in the high temperature wall interiorof the transition piece for cooling thereof and is recovered thereafter.Thus, the control of the clearance is carried out and the cooling of thetransition piece by steam is also carried out, thereby contributing inthe enhancement of the gas turbine performance.

[0026] In the invention (3), steam supply to the blade ring and that tothe transition piece are done in parallel and the same effect as that ofthe invention (2) can be obtained. Further, there is no need to providea steam supply passage from the blade ring to the transition piece butthe steam is supplied into the transition piece independently andthereby the applicability of the cooling system is broadened and anappropriate cooling system can be selected according to the types of thegas turbine.

[0027] In the invention (4), the steam first cools the blade ring andthen cools the stationary blade and the steam which has beentemperature-elevated by the cooling cools the transition piece which isa high temperature portion. Thus, not only the blade ring is cooled andthe clearance at the moving blade tip is controlled but also thestationary blade and the transition piece are cooled, therebycontributing in the enhancement of the gas turbine performance.

[0028] In the invention (5), steam supply to the blade ring and thestationary blade and that to the transition piece are done in paralleland the same effect as that of the invention (4) can be obtained.Further, the cooling system is made such that the steam supply to thetransition piece can be done by a separate system and thereby theapplicability of the cooling system is broadened and an appropriatecooling system can be selected according to the types of the gasturbine.

[0029] In the invention (6), the blade ring of the invention (2) is onlythe blade ring of the first stage which receives the severest thermalinfluence and the cooling passage is formed by the U-shape passage ineach of the blocks arranged corresponding to positions of thecombustors. Thereby, inflow of the cooling steam to the transition pieceand outflow therefrom of the cooling steam having cooled the transitionpiece both via the combustor transition piece connection portion arefacilitated and the structure therefor can be also simplified.

[0030] In the invention (7), the blade ring of the invention (2) isdivided into the first and second blade rings and the first and secondblade rings are provided with the first and second cooling passages,respectively. Thereby, the clearances at the tips of the first stage andsecond stage moving blades, respectively, can be controlled by thesteam-cooling of the blade rings and the performance of the gas turbineof the invention (2) can be enhanced further effectively.

[0031] In the invention (8), supply of the cooling steam into thetransition piece mentioned in the invention (7) is done easily throughthe transition piece cooling inlet of the combustor transition piececonnection portion and also the cooling steam having cooled thetransition piece is taken out easily through the transition piececooling outlet so as to be collected in the outlet pipe manifold andthereby the recovery of the steam can be done easily into the steamsupply source from the outlet pipe manifold.

[0032] In the invention (9), the cross sectional shape of the blade ringis approximately symmetrical relative to the radial directional centralaxis thereof so as to be compact in shape and the fitting of the bladering with the turbine casing inner wall is done easily via the recessedor protruded portion and thereby the deformation quantity of the bladering can be made smaller and equalized. Further, by making the bladering cross sectional shape compact, the fitting portion with the turbinecasing is simplified and the diameter of the turbine casing in this areacan be made smaller. Also, in the invention (10), at the flangeconnection portion of the upper and lower semicircular portions of theblade ring, the sealing material is interposed around the extendedcooling passage of the upper semicircular portion of the blade ring andthereby steam leakage in this portion can be prevented. Also, in theinvention (11), the members having the thermal balancing massessubstantially equivalent to the flanges on both of the side surfaces ofthe blade ring are provided on the upper and lower portions of the bladering and thereby distortion of the blade ring caused by heat can be madeuniform and occurrence of unusual thermal stresses can be prevented.Also, in the invention (12), the steam inlets and steam outlets of theblade ring are arranged evenly as much as possible in the vertical andhorizontal directions and thereby the thermal deformation is balancedand the thermal deformation quantity is made uniform. Also, in theinvention (13), the thermal shield is applied to the surface of theblade ring exposed to the high temperature gas and thereby the thermalinfluences given on the blade ring can be lessened.

[0033] In the invention (14), the basic inventions of (1) to (5) aboveare added with the sensors provided circumferentially in the blade ringfor sensing the clearances at the tip of the moving blade and thesignals of the clearances so sensed are inputted into the control unit.The control unit compares the clearance signals so sensed with thetarget value which is stored in advance and controls the steamtemperature by the steam temperature controller and also controls theopening of the flow control valve so that the clearances may approach tothe target value. By so controlling, the steam temperature, pressure andflow rate can be adjusted easily, the clearances are set to the targetvalue and the gas turbine performance can be prevented from beingreduced. Further, in the invention (15), the FM electrostatic capacitytype sensor is used and thereby the clearance can be detected preciselyeven in the high temperature state in the range of 0 to 5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a constructional view of a gas turbine of a firstembodiment according to the present invention.

[0035]FIG. 2 is a constructional view of a gas turbine of a secondembodiment according to the present invention.

[0036]FIG. 3 is a schematic cross sectional view showing a blade ringcooling structure and a cooling steam passage of the gas turbine of thesecond embodiment of FIG. 2.

[0037]FIG. 4 is a partially cut-out perspective view showing the bladering cooling structure and cooling steam passage of the gas turbine ofthe second embodiment of FIG. 2.

[0038]FIG. 5 is a system diagram showing another example of the bladering cooling structure of the gas turbine of the second embodiment ofFIG. 2.

[0039]FIG. 6 is a cross sectional view showing a concrete structure ofthe blade ring cooling system of FIG. 5.

[0040]FIG. 7 is an enlarged view showing a shape of a second blade ringdescribed with respect to FIGS. 5 and 6.

[0041]FIG. 8 is an enlarged view showing shapes of a turbine casing andthe second blade ring described with respect to FIG. 6.

[0042]FIG. 9 is a partial cross sectional view of a flange connectionportion of the blade ring, wherein

[0043]FIG. 9(a) shows a prior art example of the blade ring and

[0044]FIG. 9(b) shows a representative example of the second blade ringof FIG. 5.

[0045]FIG. 10 is a schematic view showing a further improvement, havingthermal balancing masses, in the blade ring of the second embodimentdescribed with respect to FIGS. 5 and 6, wherein

[0046]FIG. 10(a) is a front view of the blade ring and

[0047]FIG. 10(b) is a side view of the blade ring.

[0048]FIG. 11 is a front view of the blade ring, having steam inlets andsteam outlets, of the second embodiment described with respect to FIGS.5 and 6, wherein

[0049]FIG. 11(a) shows an example having two steam inlets and four steamoutlets and

[0050]FIG. 11(b) shows an example having three steam inlets and threesteam outlets.

[0051]FIG. 12 is a cross sectional view of a first blade ring, having athermal shield, of the second embodiment described with respect to FIGS.5 and 6.

[0052]FIG. 13 is a constructional view of a gas turbine of a thirdembodiment according to the present invention.

[0053]FIG. 14 is a constructional view of a gas turbine of a fourthembodiment according to the present invention.

[0054]FIG. 15 is a constructional view of a gas turbine of a fifthembodiment according to the present invention.

[0055]FIG. 16 is a view showing clearance characteristic curves forexplaining a clearance control system applicable to the first to fifthembodiments according to the present invention.

[0056]FIG. 17 is a cross sectional view of a gap sensor applicable tothe clearance control system described with respect to FIG. 16.

[0057]FIG. 18 is a front view of the blade ring including a crosssectional view taken on line A-A of FIG. 17.

[0058]FIG. 19 is a control diagram of the clearance control systemdescribed with respect to FIG. 16.

[0059]FIG. 20 is a cross sectional view showing an interior of arepresentative gas turbine in the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Herebelow, embodiments according to the present invention will bedescribed concretely with reference to figures.

[0061]FIG. 1 is a constructional view of a gas turbine of a firstembodiment according to the present invention. In FIG. 1, numeral 1designates a gas turbine, numeral 2 designates a compressor and numeral3 designates a combustor. In the gas turbine 1, there is provided ablade ring cooling passage 8. Cooling steam coming from a steam turbinebottoming cycle 10 is supplied into the blade ring cooling passage 8 viaa piping 6 for cooling a blade ring and the steam after used for thecooling and heated is returned to be recovered into the steam turbinebottoming cycle 10 via a piping 7. Also, at the rise time, steam of anappropriate temperature coming from an auxiliary boiler 11 is suppliedinto the blade ring cooling passage 8 via a piping 4 for cooling theblade ring and the steam after used for the cooling is recovered intothe auxiliary boiler 11 via a piping 5. The blade ring is so cooled bysteam and thereby thermal elongation changes of the blade ring areadjusted so that a clearance between the blade ring and a moving blademay not be enlarged.

[0062]FIG. 2 is a constructional view of a gas turbine of a secondembodiment according to the present invention, wherein a cooling systemof a gas turbine blade ring and that of a gas turbine combustortransition piece are connected in series to each other. In FIG. 2,cooling steam coming from a steam turbine bottoming cycle 10 is firstsupplied into a blade ring cooling passage 8 via a piping 12 for coolingthe blade ring and the steam after used for the cooling enters atransition piece cooling passage 9 of a combustor 3 via a piping 13 forcooling the transition piece and the steam having cooled the transitionpiece is recovered into the steam turbine bottoming cycle 10 via apiping 14.

[0063]FIG. 3 is a schematic cross sectional view showing a blade ringcooling structure and a cooling steam passage of the gas turbine of thesecond embodiment of FIG. 2, wherein a steam-cooling is applied to theblade ring of a first stage moving blade which receives the severestthermal influence in the gas turbine and the steam having cooled theblade ring is flown into the transition piece for cooling thereof.

[0064] In FIG. 3, there is provided a blade ring 20 of the gas turbine,being fixed to a turbine casing inner wall and surrounding a first stagemoving blade IS. A steam inlet 21 is provided in the blade ring 20 andcooling steam flows through the steam inlet 21 to be supplied into theblade ring 20 via the piping 12. The cooling steam supplied into theblade ring 20 flows through the blade ring cooling passage 8 for coolingthe blade ring 20 and the steam having cooled the blade ring 20 flowsthrough the piping 13 to be led into the transition piece coolingpassage 9 of the combustor 3. The steam having cooled the transitionpiece is recovered via a piping which is not shown.

[0065]FIG. 4 is a partially cut-out perspective view showing a coolingstructure of the blade ring 20, which confronts the first stage movingblade 1S, of the gas turbine of the second embodiment of FIG. 2. In FIG.4, there is provided a steam supply pipe 25 along an innercircumferential wall of the blade ring 20. The blade ring 20 asillustrated here shows only a semi-circular upper half portion thereof,wherein there are provided one steam inlet 21 and two steam outlets 24and the steam inlet 21 and each of the steam outlets 24 are connectedwith the steam supply pipe 25 and a steam recovery pipe 26,respectively. The steam supply pipe 25 bifurcates from the steam inlet21 toward both side directions thereof and the pipe diameter thereofbecomes gradually smaller toward downstream of the steam supply pipe 25.The reason for that is to maintain a uniformity in the steam flowpressure in the pipe as the steam flow rate becomes less toward thedownstream side when the steam is supplied to a plurality of blade ringcooling portions 22, each being formed in a block shape.

[0066] Also, on the reverse side of the member of the blade ring coolingportion 22, there is formed a transition piece cooling system connectionportion 23 and this transition piece cooling system connection portion23 is arranged in eight pieces circumferentially on the transition pieceside of the blade ring 20 so as to position correspondingly to each ofthe combustors. In the transition piece cooling system connectionportion 23, there are provided a hole 27 which connects to a steaminflow port of the transition piece and a hole 28 which connects to asteam outflow port of the transition piece.

[0067] In the cooling structure shown in FIG. 4, cooling steam flows infrom the steam inlet 21 and, being bifurcated toward both sides thereof,enters respectively the blade ring cooling passage 8 of the blade ringcooling portion 22. The blade ring cooling passage 8 comprises twopassages 8 a arranged in the axial direction of the turbine and apassage 8 b arranged in the circumferential direction of the turbine andwhen the cooling steam flows therethrough, it cools the circumferentialwall surface portion, confronting the moving blade, of the blade ring20.

[0068] The cooling steam flows through the blade ring cooling passage 8from one of the passages 8 a to the passage 8 b and further to the otherof the passages 8 a and then flows through the hole 27 of the transitionpiece cooling system connection portion 23 to enter the transition pieceof the combustor (not shown) for cooling thereof. The steam havingcooled the transition piece returns to the hole 28 of the transitionpiece cooling system connection portion 23 from the transition piece andthen flows into the steam recovery pipe 26 to be recovered through thesteam outlet 24.

[0069] Thus, in the gas turbine of the present second embodiment, theblade ring, confronting the moving blade, is cooled by steam so as tosuppress thermal influences and, by controlling flow rate, pressure andtemperature of the steam appropriately, contact at the clearance portionbetween the blade ring and the moving blade tip is prevented and theclearance is maintained as small as possible in operation. Also, thesteam having cooled the blade ring 20 is flown into the transition pieceof the combustor 3, which is of a higher temperature, and thereby thetransition piece is cooled effectively and the gas turbine performancecan be enhanced.

[0070]FIG. 5 is a system diagram showing another example of the bladering cooling structure of the gas turbine of the second embodiment ofFIG. 2. In this example, independent blade rings confronting the firststage moving blade and the second stage moving blade, respectively, areprovided, that is, the structure is made such that the conventionalblade ring, made in an integral structure, is separated so that therespective blade rings are featured in the shape having less thermalinfluences.

[0071] In FIG. 5, cooling steam coming from a boiler first flows into asecond blade ring 31 for cooling thereof and then flows into a firstblade ring 30 for cooling thereof. The steam having cooled the first andsecond blade rings 30, 31 flows into a transition piece cooling inlet 32to flow through a wall interior of the transition piece for cooling thetransition piece. The steam having cooled the transition piece flowsinto an outlet pipe manifold 34 through a transition piece coolingoutlet 33 and is recovered into a steam turbine.

[0072]FIG. 6 is a cross sectional view showing a concrete structure ofthe blade ring cooling system shown in FIG. 5. In FIG. 6, the firstblade ring 30 and the second blade ring 31 are separated from each otherand the first blade ring 30 confronts the first stage moving blade 1Sand the second blade ring 31 confronts the second stage moving blade 2S.In the blade rings 30, 31, along the circumferential central portionthereof, there are provided blade ring cooling passages 35, 36,respectively, and the first blade ring 30 and the second blade ring 31are connected to each other with three passages arranged in the axialdirection of the turbine, as schematically shown in FIG. 5.

[0073] The blade ring cooling passage 35 in the first blade ring 30 isconnected to the transition piece cooling inlet 32 with a plurality ofpassages 38 arranged in the axial direction and steam is supplied into awall interior of the transition piece through the passages 38 and thetransition piece cooling inlet 32. The steam having cooled thetransition piece flows through the transition piece cooling outlet 33and a piping 39 and further through the outlet pipe manifold 34 and isreturned to a steam turbine. Also, on the circumferential surfaces andon both side surfaces thereof of the first and second blade rings 30,31, respectively, there are provided thermal shields 37, so that theblade rings 30, 31 may be shielded from heat transferring in the axialdirection.

[0074]FIG. 7 is an enlarged view showing the second blade ring 31described with respect to FIGS. 5 and 6. The second blade ring 31 isconstructed such that the conventional blade ring 103 is separated intotwo parts so that one of the parts constitutes the second blade ring 31and the blade ring cooling passage 36 is formed in the second blade ring31 along the circumferential interior central portion thereof. Thesecond blade ring 31 comprises a recessed portion 31 a which fits to aportion of the turbine casing wall and another recessed portion 31 bwhich constitutes a fitting portion on the moving blade side and theserecessed portions 31 a, 31 b, respectively, are formed approximately ina front and rear symmetrical shape relative to the turbine radialdirectional central axis of the second blade ring 31 in FIG. 7. Byemploying such construction of the central axis symmetry, the blade ringcan be made compact in the shape and deformation quantity around thecentral axis can be made uniform.

[0075] The first blade ring 30 is also made in the substantially sameconstruction and description thereon will be omitted. By employing thefirst and second blade rings 30, 31 constructed as mentioned above, thedeformation quantity around the central axis thereof can be made uniformand less as compared with the conventional blade ring 103. It is to benoted that while the recessed portion 31 a for fitting with the turbinecasing wall is formed to be recessed toward the blade ring side in theillustration, this may be reversed, that is, the turbine casing side isrecessed and the blade ring side is protruded, so that the same centralaxis symmetry may be achieved.

[0076]FIG. 8 is an enlarged view showing the turbine casing portion andthe blade ring portion shown in FIG. 6. In FIG. 8, the first and secondblade rings 30, 31 are made compact in size and the steam cooledstructure is employed and thereby a turbine casing 40 can be madesmaller as compared with a conventional turbine casing 150. Also, thefitting portion with the turbine casing wall is moved toward the innerside of the turbine so that the turbine casing outer diameter may bemade smaller and rigidity against thrust forces of the blade rings 30,31 can be enhanced as compared with the conventional case. In FIG. 8,numeral 30 a designates a first ring segment, which is a comparativelythin member fixed to the lower portion of the first blade ring 30between the first blade ring 30 and the corresponding blade tip. Numeral31 a designates a second ring segment, which is formed and arranged,like the first ring segment 30 a, between the second blade ring 31 andthe corresponding blade tip. The clearance or gap between the blade ringand the blade tip is actually that between the ring segment and thecorresponding blade tip.

[0077]FIG. 9 is a cross sectional view of a flange connection portion ofupper half and lower half portions of the blade ring and FIG. 9(a) showsa conventional example of the blade ring 103 and FIG. 9(b) shows arepresentative example of the second blade ring 31 of the secondembodiment according to the present invention. As described with respectto FIG. 7, the blade ring 31 is structured so as to mitigate localstresses by making the blade ring 31 in the central axis symmetricalshape and making the thickness uniform and also a flange 41 of the bladering 31 is made thinner as compared with a flange 151 of theconventional example. By employing such construction, both of theturbine axial directional and circumferential directional deformationquantity can be made uniform. Further, the blade ring cooling passage 36at the flange connection portion is connected via a connection portion42 and a seal 43 is interposed around the connection portion 42.

[0078]FIG. 10 is a schematic view showing a further improvement in theblade ring of the second embodiment as described with respect to FIGS. 5and 6, taking example of the first blade ring 30, and FIG. 10(a) is afront view of the blade ring and FIG. 10(b) is a side view of the same.In FIGS. 10(a) and (b), the upper half and lower half portions of thefirst blade ring 30 are fixed to each other via the horizontal flanges41 provided on both sides of the blade ring 30 and steam flows in thefirst blade ring 30 for cooling thereof and then flows into thetransition piece of the combustor 3 for cooling thereof and isrecovered. On the top and bottom of the blade ring 30, there areprovided thermal balancing masses 44. The thermal balancing masses 44have the equivalent masses to the horizontal flanges 41 so that theweight and shape may be made equivalent in the vertical and horizontaldirections and thereby thermal changes may be balanced in the samedirections.

[0079]FIG. 11 is a front view of the second blade ring 31 of the secondembodiment described with respect to FIGS. 5 and 6, showing examples ofarrangements of the steam inlet and outlet for effecting uniform andeven thermal changes and FIG. 11(a) shows an example where two steaminlets and four steam outlets are arranged and FIG. 11(b) shows anexample where three steam inlets and three steam outlets are arranged.In FIG. 11(a), the steam inlet through which steam enters the blade ring31 is arranged as two steam inlets 45-1, 45-2 at the top and bottom ofthe blade ring 31 and the steam outlet through which the steam flows outof the blade ring 31 is arranged as four steam outlets, that is, two46-1, 46-2 on the right hand side and two 46-3, 46-4 on the left handside of the blade ring 31 and the construction is made such that thearrangement of the steam inlets and outlets is balanced so as to realizea uniform and even cooling by steam, suppressing imbalances in thethermal deformation.

[0080] The example of FIG. 11(b) is for the case where a larger flowrate of the steam is needed and the steam inlet is arranged as threesteam inlets, that is, one 47-1 on the top and two 47-2, 47-3 on thelower side of the blade ring 31 and the steam outlet is arranged also asthree steam outlets, that is, two 48-1, 48-3 on the upper side and one48-2 on the lower side of the blade ring 31. Thereby, the flow of thesteam is made uniform, cooling of the blade ring by steam is equalizedand the thermal deformation quantity can be made uniform.

[0081]FIG. 12 is a cross sectional side view of the first blade ring 30of the second embodiment described with respect to FIGS. 5 and 6,showing a concrete example of the thermal shield. In FIG. 12, a thermalshield 37 is provided mainly on the front and rear side surfaces of theblade ring 30 which face to the turbine axial direction. The thermalshield 37 is fitted to the surfaces of the blade ring 30 such that aheat insulating material 49 is fixed to the surfaces by a bolt 51 and acover 50 is applied to surfaces of the heat insulating material 49. Byso applying the thermal shield 37 on the circumferential front and rearside surfaces of the blade ring 30, the blade ring 30 is shielded from ahigh temperature heat transferring in the turbine axial direction andthe effect of the steam-cooling is enhanced.

[0082] In the second embodiment as described above with respect to FIGS.2 to 12, the cooling system is so made that the blade ring 20 is cooledby steam or the second blade ring 31 is first cooled and the first bladering 30 is then cooled by steam and the steam having cooled the bladering cools the transition piece and also the construction is so madethat the blade ring 30, 31 is made compact in the central axissymmetrical shape and the thermal shield 37 is applied as well as thethermal balancing mass 44 is fitted to the blade ring 30, 31 so as toensure a balance in the thermal changes or the arrangement of the steaminlet and outlet of the blade ring 30, 31 is balanced in the verticaland horizontal directions of the blade ring 30, 31 so as to ensure auniform cooling effect. By employing such construction, the blade ringconfronting the moving blade is cooled effectively by steam and, bycontrolling the temperature, pressure and flow rate of the steam, theclearance at the moving blade tip is prevented from contacting at therise time and also the clearance is maintained as small as possibleduring the operation. Thus, the gas turbine performance can be enhanced.

[0083] Next, FIG. 13 is a constructional view of a gas turbine of athird embodiment according to the present invention. In FIG. 13, what isdifferent from the second embodiment shown in FIG. 2 is that, while thesecond embodiment employs a series cooling system in which cooling steamfirst cools the blade ring of the gas turbine 1 and then cools thetransition piece of the combustor 3, in the present third embodiment,the blade ring cooling passage 8 of the gas turbine 1 and the transitionpiece cooling passage 9 of the combustor 3 are connected in parallel toeach other and the cooling steam flows into them concurrently. Otherportions of the construction are same as those of the second embodimentshown in FIG. 3.

[0084] In FIG. 13, cooling steam coming from the steam turbine bottomingcycle 10 flows in parallel into the transition piece cooling passage 9of the combustor 3 via a piping 17 and into the blade ring coolingpassage 8 of the gas turbine 1 via a piping 15, respectively, and thesteam after used for the cooling flows from the transition piece via apiping 18 and from the blade ring via a piping 16 to be both recoveredinto the steam turbine bottoming cycle 10. It is to be noted that, as tothe present third embodiment also, except the blade ring coolingstructure in which the cooling steam having cooled the blade ring is notsupplied into the transition piece but is recovered as it is, the sameconcrete constructions shown in FIGS. 3 to 12 may be applied to thethird embodiment as they are and, in this case also, the same effect ofthe invention can be obtained.

[0085]FIG. 14 is a constructional view of a gas turbine of a fourthembodiment according to the present invention, wherein the coolingsystem of the blade ring and the transition piece is made such thatcooling steam first cools the blade ring, which confronts the firststage moving blade 1S, and then cools the first stage stationary blade1C and the steam further flows into the transition piece for coolingthereof and is then recovered.

[0086] In FIG. 14, cooling steam is led from a steam turbine bottomingcycle (not shown), like in FIGS. 1 and 2, via a passage 61 and enters aportion 60 a, confronting the first stage moving blade IS, of a bladering 60 for cooling thereof. Cooling of this portion 60 a, like in theexample shown in FIG. 4, may be done by a cooling passage formed in aU-shape by the turbine axial directional and radial directionalpassages. The steam having cooled the portion 60 a of the blade ring 60flows into the first stage stationary blade 1C for cooling thereof via apassage 62 and then flows into the transition piece of the combustor 3for cooling thereof via a passage 63 and is thereafter recovered via apassage 64.

[0087] In the fourth embodiment described above, like in the secondembodiment, the blade ring is cooled by steam so that the clearancebetween the blade ring and the moving blade IS may be adjusted to anappropriate gap as well as the transition piece is cooled by the steamhaving cooled the blade ring and, moreover, the steam before enteringthe transition piece cools the first stage stationary blade 1C as well.Hence, the cooling effect is enhanced and the gas turbine performance isalso enhanced.

[0088]FIG. 15 is a constructional view of a gas turbine of a fifthembodiment according to the present invention. If the fifth embodimentis compared with the fourth embodiment shown in FIG. 14, while in thefourth embodiment, cooling of the blade ring 60 and the stationary blade1C and that of the transition piece are done sequentially in series, inthe present fifth embodiment, cooling of the blade ring 60 and thestationary blade 1C and that of the transition piece are done inparallel and other portions of the construction are same as those of thefourth embodiment of FIG. 14.

[0089] That is, in FIG. 15, cooling steam enters the blade ring 60 viathe passage 61 for cooling the portion 60 a of the blade ring 60 andthen enters the stationary blade 1C for cooling thereof via the passage62 and the steam having cooled the stationary blade 1C is recovered viaa passage 63′. At the same time, the steam bifurcates from the passage61 to enter the transition piece for cooling thereof via a passage 65and is then recovered via a passage 66. Thus, cooling of the blade ring60 and the stationary blade 1C and that of the transition piece arecarried out in parallel. In the so constructed fifth embodiment also,the same effect as that of the fourth embodiment can be obtained.

[0090] Next, a clearance control system applicable to the first to fifthembodiments according to the present invention will be described withreference to FIGS. 16 to 19. FIG. 16 is a view showing clearancecharacteristic curves, wherein (X) shows the clearance characteristiccurve when the clearance control system of the present invention isapplied and (Y) shows the clearance characteristic curve in the priorart. In the curve of (Y) of the conventional case, the initial clearanceCR1 is 5 mm at a cold start time and 3 mm at a hot start time and alsothe minimum clearance CR2 at time T₁ is 3 mm at the cold start time and0.8 mm at the hot start time.

[0091] At the rise time of the operation, while the blade ring is cold,the moving blade is heated earlier so as to make a larger thermalelongation and the clearance is reduced so that the minimum clearanceCR2 occurs at the time T₁. In the characteristic curve (Y) of theconventional case, if the initial clearance CR1 is too small, then thereoccurs a contact in the minimum clearance CR2 at the time T₁ so as tocause a dangerous state and hence the initial clearance CR1 must be setwith a certain allowance. In the conventional characteristic curve (Y),as the clearance increases in the operation, as shown in FIG. 16, if theinitial clearance is made too large, then the clearance in the operationwill become too large so that the gas turbine performance may bereduced.

[0092] On the contrary, in the characteristic curve (X) of the presentinvention, the blade ring is also heated at the rise time by steam ofthe auxiliary boiler, as shown in FIG. 1, so as to make a thermalelongation and the initial clearance also becomes large. Hence, theminimum clearance at the time T₁ becomes large, so that the risk ofcontact can be avoided. In operation, as described above with respect tothe first to fifth embodiments, the blade ring is cooled by steam andthe temperature, pressure and flow rate of the steam are controlled, asdescribed later, so that the clearance may be set to an optimal targetvalue CR0, which takes account of a safety and thereby the operation isdone with the optimal clearance CR0 being maintained and the gas turbineperformance is prevented from being reduced.

[0093]FIG. 17 is a cross sectional view of a gap sensor applicable tothe clearance control system of the blade ring described with respect toFIG. 16. In FIG. 17, a gap sensor 70 is inserted from outside of theturbine casing 40 to pass through the turbine casing 40 and the bladering 30 and to be fitted so that a sensing portion of the gap sensor 70may be exposed on a surface of a shroud 30 a on the first stage movingblade side. The gap sensor 70 is an FM (frequency modulation)electrostatic capacity type sensor and has a measuring performance up tothe maximum usable temperature of 1200° C. with an error of about 0.1 mmfor the measuring range of 0 to 5.5 mm.

[0094]FIG. 18 is a front view of the turbine casing and the blade ring,wherein each of the partially cut out portions shows a cross 5 sectionalview taken on line A-A of FIG. 17. As shown in FIG. 18, four pieces ofthe gap sensors 70 are inserted from outside of the turbine casing 40 topass through the turbine casing 40 and the blade ring 30 and the sensingportion of the gap sensor 70 is exposed on the surface of the shroud 30a of the blade ring 30, 10 which confronts the first stage moving blade,and thereby the gap at the moving blade tip is detected at four placesand the vertical directional and horizontal directional gaps of theblade ring are measured by the so detected four values, so that thecharacteristic curve as shown in FIG. 16 can be obtained. It is to benoted that is such measuring is likewise carried out on the gap at thesecond stage moving blade tip.

[0095]FIG. 19 is a control diagram of the clearance control systemapplicable to the first to fifth embodiments according to the presentinvention. In FIG. 19, steam coming from the steam turbine 20 bottomingcycle 10 has its temperature controlled by a temperature controller 72and has its pressure and flow rate controlled by a flow control valve 71and then flows into the blade ring 30 for cooling thereof through upperand lower two steam inlets of the blade ring 30. The steam having cooledthe blade ring 30 flows out 25 of four steam outlets of the blade ring30 to be recovered into the steam turbine bottoming cycle 10. Also, inthe blade ring 30, there are provided the four gap sensors 70, as shownin FIG. 18, and thereby the clearance at the moving blade tip ismeasured and the signal thereof is inputted into a control unit 73.

[0096] The control unit 73 takes the signal from the gap sensor 70 andwhen the time T₁ in the rise time, as shown in FIG. 16, has passed, thecontrol unit 73 compares the signal with the optimal target value of theclearance, which is stored in advance, and thereby the opening of theflow control valve 71 and thus the pressure and flow rate of the steamare controlled so that the clearance approaches to the target value aswell as the temperature controller 72 and thus the temperature of thesteam are likewise controlled.

[0097] By controlling the temperature, pressure and flow rate of thesteam at the control unit 73, conditions of the steam-cooling of theblade ring are variously changed so that the clearance may be approachedto the optimal target value, as shown in FIG. 16, and thereby theclearance can be set as small as possible and reduction in the gasturbine performance due to enlargement of the clearance can beprevented.

[0098] While the preferred forms of the present invention have beendescribed, it is to be understood that the invention is not limited tothe particular constructions and arrangements herein illustrated anddescribed but embraces such modified forms thereof as come within thescope of the appended claims.

What is claimed is:
 1. A gas turbine comprising a moving blade and ablade ring confronting a tip of said moving blade, wherein a coolingpassage is provided in said blade ring and an auxiliary boiler and asteam supply source connecting to a steam turbine bottoming cycle areconnected to said cooling passage, so that steam of said auxiliaryboiler or said steam supply source is flown into said cooling passagefor cooling said blade ring and the steam having cooled said blade ringis recovered, and thereby a clearance between said tip of the movingblade and said blade ring is reduced.
 2. A gas turbine comprising amoving blade and a blade ring confronting a tip of said moving blade aswell as comprising a combustor and a transition piece contained in saidcombustor, wherein a cooling passage is provided in said blade ring, sothat steam of a steam supply source is flown into said cooling passagefor cooling said blade ring and the steam having cooled said blade ringis flown into said transition piece via a combustor transition piececonnection portion for cooling a wall interior of said transition pieceand the steam having cooled said wall interior of the transition pieceis recovered into said steam supply source, and thereby a clearancebetween said tip of the moving blade and said blade ring is reduced. 3.A gas turbine comprising a moving blade and a blade ring confronting atip of said moving blade as well as comprising a combustor and atransition piece contained in said combustor, wherein a cooling passageis provided in said blade ring, so that steam of a steam supply sourceis flown in parallel into said cooling passage for cooling said bladering and into said transition piece via a combustor transition piececonnection portion for cooling a wall interior of said transition pieceand the steam having cooled said blade ring and said wall interior ofthe transition piece is recovered into said steam supply source, andthereby a clearance between said tip of the moving blade and said bladering is reduced.
 4. A gas turbine comprising a first stage stationaryblade and a first stage moving blade and a blade ring confronting a tipof said first stage moving blade as well as comprising a combustor and atransition piece contained in said combustor, wherein a blade ringcooling passage is provided in said blade ring and a stationary bladecooling passage is provided in said first stage stationary blade so asto connect to said blade ring cooling passage, so that steam of a steamsupply source is flown into said blade ring cooling passage for coolingsaid blade ring and the steam having cooled said blade ring is flowninto said stationary blade cooling passage for cooling said first stagestationary blade and the steam having cooled said first stage stationaryblade is flown into said transition piece via a combustor transitionpiece connection portion for cooling a wall interior of said transitionpiece and the steam having cooled said wall interior of the transitionpiece is recovered into said steam supply source, and thereby aclearance between said tip of the first stage moving blade and saidblade ring is reduced.
 5. A gas turbine comprising a first stagestationary blade and a first stage moving blade and a blade ringconfronting a tip of said first stage moving blade as well as comprisinga combustor and a transition piece contained in said combustor, whereina blade ring cooling passage is provided in said blade ring and astationary blade cooling passage is provided in said first stagestationary blade so as to connect to said blade ring cooling passage, sothat steam of a steam supply source is flown in parallel into said bladering cooling passage for cooling said blade ring and into saidstationary blade cooling passage for cooling said first stage stationaryblade and the steam having cooled said first stage stationary blade isflown into said transition piece via a combustor transition piececonnection portion for cooling a wall interior of said transition pieceand the steam having cooled said blade ring and said wall interior ofthe transition piece is recovered into said steam supply source, andthereby a clearance between said tip of the first stage moving blade andsaid blade ring is reduced.
 6. A gas turbine as claimed in claim 2 ,wherein said blade ring is a blade ring confronting a tip of a firststage moving blade, said combustor is a plurality of combustors arrangedin a turbine circumferential direction, there are provided in said bladering a plurality of blocks protruding in a turbine axial direction frompositions of said blade ring corresponding to positions of saidplurality of combustors and, in each of said plurality of blocks, thereis provided a U-shape passage formed by turbine axial directional andcircumferential directional passages, so that steam is flown into saidU-shape passage from one end of said U-shape passage for cooling saidblade ring and is flown out of the other end of said U-shape passage,and the steam having cooled said blade ring is supplied into saidtransition piece via said combustor transition piece connection portion.7. A gas turbine as claimed in claim 2 , wherein said blade ringcomprises a first blade ring confronting a first stage moving blade anda second blade ring confronting a second stage moving blade, saidcooling passage comprises a first cooling passage formed in said firstblade ring and a second cooling passage formed in said second blade ringand there are provided a turbine axial directional passage forconnecting said first and second cooling passages to each other and atransition piece side passage for connecting said first cooling passageand said combustor transition piece connection portion to each other, sothat the steam of said steam supply source is flown sequentially in saidsecond cooling passage, turbine axial directional passage, first coolingpassage and transition piece side passage and is then supplied to saidcombustor transition piece connection portion.
 8. A gas turbine asclaimed in claim 7 , wherein said combustor transition piece connectionportion comprises a transition piece cooling inlet connecting to saidfirst cooling passage, a transition piece cooling outlet through whichthe steam having cooled said transition piece flows out and an outletpipe manifold connecting to said transition piece cooling outlet.
 9. Agas turbine as claimed in claim 7 , wherein each of said first andsecond blade rings is formed such that upper and lower two separatedsemicircular portions of the blade ring are joined together at flangesprovided on both side surface portions of the blade ring, there areprovided a recessed portion or a protruded portion on an outercircumferential surface portion of the blade ring so as to fit to or fitin a portion of a turbine casing inner wall and another protrudedportion on an inner circumferential surface portion of the blade ring soas to support a wall surface confronting said tip of the moving bladeand a turbine axial directional cross sectional shape of the blade ringis approximately symmetrical relative to a turbine radial directionalcentral axis in said turbine axial directional cross sectional shape ofthe blade ring.
 10. A gas turbine as claimed in claim 7 , wherein eachof said first and second blade rings is formed such that upper and lowertwo separated semicircular portions of the blade ring are joinedtogether at flanges provided on both side surface portions of the bladering and, in horizontal surface portions of said upper and lowersemicircular portions of the blade ring so joined at said flanges, thecooling passage provided in said upper semicircular portion of the bladering is extended so as to be inserted with a predetermined length intothe cooling passage provided in said lower semicircular portion of theblade ring and a sealing material is interposed around the coolingpassage so extended of said upper semicircular portion of the bladering.
 11. A gas turbine as claimed in any one of claims 1 to 5 , whereinsaid blade ring is formed such that upper and lower two separatedsemicircular portions of said blade ring are joined together at flangesprovided on both side surface portions of said blade ring and there areprovided members, having masses substantially equivalent to said flangesthermally, on upper and lower portions of an outer circumferentialsurface portion of said blade ring.
 12. A gas turbine as claimed in anyone of claims 1 to 5 , wherein said blade ring is provided with aplurality of steam inlets and steam outlets, respectively, arrangedsubstantially evenly in vertical and horizontal directions on an outercircumferential surface portion of said blade ring.
 13. A gas turbine asclaimed in claim 7 , wherein said blade ring is applied to on itssurface exposed to a high temperature space with a thermal shield madeof a heat insulation material.
 14. A gas turbine as claimed in any oneof claims 1 to 5 , wherein said blade ring is provided therein with aplurality of sensors for sensing said clearance at the tip of the movingblade, said sensors being inserted from outside of a turbine casing topass through said turbine casing and said blade ring so that sensingportions of said sensors may be exposed on an inner circumferential wallsurface confronting said tip of the moving blade, and there are provideda steam temperature controller arranged in a route for supplying saidblade ring with steam from said steam supply source, a steam flowcontrol valve arranged between said steam temperature controller and asteam inlet of said blade ring and a control unit taking signals fromsaid sensors for comparison with a predetermined target value andcontrolling said steam temperature controller and an opening of saidsteam flow control valve so that said clearance may be approached tosaid target value.
 15. A gas turbine as claimed in claim 14 , whereinsaid sensors are FM electrostatic capacity type sensors.